Set a default for settings.AJAX_SERIAL when running unit tests.

The change to prevent extension reloading during tests needed an
accompanying trivial change to set settings.AJAX_SERIAL. This wasn't set
before, and unit tests depended on it. We were getting a working value,
though, because ExtensionManager recalculates it when loading
extensions.
Add a profile field controlling whether users want to receive email.

Not everyone wants to get emails from Review Board. This change adds a flag to
the profile to control whether users will get anything directly addressed to
them.

This implementation was done on release-2.0.x because of the testing
infrastructure, but I also plan to backport this to release-1.7.x

Testing done:
* Ran unit tests
* Tested database evolution.
* Tested the account settings.

Reviewed at https://reviews.reviewboard.org/r/5907/
Merge branch 'release-2.0.x'
Add a profile field controlling whether users want to receive email.

Not everyone wants to get emails from Review Board. This change adds a flag to
the profile to control whether users will get anything directly addressed to
them.

This is the release-1.7.x version of the change.

Testing done:
* Ran unit tests
* Tested database evolution.
* Tested the account settings.

Reviewed at https://reviews.reviewboard.org/r/5908/
Merge branch 'release-1.7.x' into release-2.0.x
Fix building API docs due to the Djblets object caching change.

Djblets's WebAPIResource now sets request._djblets_webapi_object_cache
when being called as a view. However, the webapi doc generation code
bypasses this, resulting in a breakage when building docs.

We now set this on our DummyRequest manually, in order to give the
Djblets functions something to work with.

Reviewed at https://reviews.reviewboard.org/r/5918/
Merge branch 'release-2.0.x'
Fix building web API docs with the latest changes on master.

This fixes up the initial_data fixture for the docs database for the new
"email_list_only" field on Group, and for the way in which
local_site_name was fetched in HostingServiceResource.

Reviewed at https://reviews.reviewboard.org/r/5919/